Lecture-15 - Lecture 15 Earthquake Prediction Tuesday,...

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1 Lecture 15 – Earthquake Prediction Tuesday, October 28t h , 200 8 EARTHQUAKE PREDICTION To successfully predict an earthquake we would like to know:- ± PLACE ± TIME ± MAGNITUDE (rather like a weather forecast)
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2 Evidence must be integrated from a variety of sources, including:- ± GEOLOGICAL EVIDENCE ± STATISTICAL INFORMATION ± SEISMIC MEASUREMENTS ± PHYSICAL MEASUREMENTS ± Other Information Geological Evidence From a knowledge of the geology, and geological processes, in an area, combined with previous earthquake records, we can prepare earthquake hazard maps. Remember, the geological past is a guide to the future.
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3 The information for earthquake hazard maps includes:- ± Geology of the area including, landslides, ground settling, water-logged and poorly consolidated rocks. ± Location of active and inactive faults. ± Types of faults ± Evidence for recent fault movement ± The earthquake history of the area ± Location of previous earthquake epicenters ± Determination of previous earthquake intensities ± Correlation of earthquakes with local faults Statistical Information There appears to be a rough relationship between the magnitude of an earthquake and the length of fault that ruptures:- Magnitude (Richter) Rupture Length (miles) 5.5 3 - 6 6.0 6 – 9 6.5 9 – 18 7.0 18 – 36 7.5 36 – 60 8.0 60 - 120 In other words if we could predict what part of a fault was likely to rupture, we could estimate the magnitude of the forthcoming earthquake.
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Frequency of Earthquakes Most attempts to predict the frequency of earthquakes rely on the assumption that the forces creating earthquakes are constant and long-lived. [i.e. the slow but inexorable movement of the plates] EXAMPLE: San Francisco 1906 (Reid) Movement over 50 years = 10 feet (prior to the earthquake) Therefore, years/foot movement = 5 years Movement during earthquake = 20 feet Predicted Frequency (20 x 5) = 100 years CONCLUSION : There might be an earthquake on this part of the San Andreas fault every 100 years or so. Parkfield Parkfield is located on a 15 mile segment of the San Andreas fault. Small earthquakes (5.5 – 5.6) have occurred here regularly, almost every 22 years. As a consequence of this regularity it has been under intense scrutiny
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This note was uploaded on 08/09/2009 for the course GEOSCIENCE GEO-105 taught by Professor Rhodes during the Fall '08 term at UMass (Amherst).

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Lecture-15 - Lecture 15 Earthquake Prediction Tuesday,...

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